1. Field of the Invention
This invention relates to motor control circuits and, more particularly, to motor control circuit signals for operating a motor to rotate a shaft in a predetermined direction until the motor circuit provides a high frequency control signal for substantially stopping motor operation.
2. Description of the Prior Art
Control circuits for a reversible motor have included a pair of Triacs which are switched into operation by signals derived from a controller circuit, whereby, activation of one Triac causes a motor shaft to rotate in a clockwise direction and activation of the other Triac causes the motor shaft to rotate in a counter-clockwise direction. The controller circuit included means for providing a signal for activating a selected Triac. For example, prior art controller circuits included a difference amplifier having a first input terminal coupled to a transducer and a second input terminal coupled to a variable reference signal. The transducer is arranged to sense an angular displacement to the motor shaft from a reference position and to provide a corresponding electrical signal to the first input terminal of the difference amplifier. The output signal from the difference amplifier is proportional to the difference in magnitude between the reference and transducer electrical signals. Relatively complex and expensive circuitry convert the differential amplifier output signal into control signals suitable for operating a selected Triac. No output signal is provided by the difference amplifier when the magnitude of the reference and transducer electrical signals are substantially equal. The motor is inoperative in the absense of a difference amplifier output signal.
It is therefore desirable to arrange relatively simple circuitry to form a control circuit to provide suitable signals for operating a reversible motor.